Maybe it should be the other way around, so allow Norse, but remove Norman. Since those conditions will apply the whole game period; this might seem nice for a 867 game, but for games started in 1066 and later that won't be ideal.
@ Jorlem: unless a ruler with an Arabic culture converts to Christianity, this is basically the only kingdom they can create in this region since (almost all) other Iberian kingdoms require having a religion from the Christian Group; unlike the Christian rulers, who have some options to choose from here, but must adopt Arabic culture, if they want to create that title.